We have had this issue crop up randomly on several worlds in 1.11.4 (Windows 10 edition); when taming a new cat the seated cat will scoot around at running speed, and if unseated will run around wildly at random. The behavior isn't changed by feeding the cat, or breeding the cat. The cat can be contained in a boat or minecart.
It seems to have resolved itself. After we joined one of her games, all of a sudden she could then log on to our worlds without the error message. Thanks!
We are still having this same issue on Windows 10. Leather armor (plain or colored) is white on armor stands.